pmdadm: minor tweak GNUmakefile targets for dmstats
pmdadm: minor tweak GNUmakefile targets for dmstats

Nathan's previous commit added dmstats.[ch] to src/pmdas/dm/GNUmakefile
but Fukiyama has called these files dm.[ch].

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp